In radiotelephone systems such as the Global System for Mobile Communications (GSM) radiotelephone system in use in Europe, a SIM card is inserted into a radiotelephone for providing subscriber identification, billing information and other information concerning the operation of the radiotelephone. The SIM is a key component of the GSM and typically comprises a smart card which is inserted into a GSM phone in order to make the phone work.
In a typical cellular telephone communication system, each subscriber unit is assigned a mobile subscriber (MSI) which uniquely identifies the subscriber unit from other subscriber units. In the European cellular communication system, one such identifier is the international mobile subscriber identification number (IMSI). To protect the privacy of the BMSI.
It is highly desirable to provide a personal communication system which has a single personal telecommunications device which is operable in all available cellular systems, e.g., AMPS, TDMA, CDMA, GSM, etc. across all available cellular frequencies, e.g., 900 MHz or 1800 MHz as well as satellite frequencies, and which operates like an inexpensive cordless phone when the user is at home.
In conjunction with such an approach the user has a single phone number, and that phone number tracks that phone such that wherever the phone is, that is where the user is.
In the SIM environment, a user is not constrained to carry his own personal communications device on him at all times, since it is SIM plus a generic, non-user specific communications device which the system sees, as opposed to a specialized, user specific device such as a conventional wireline phone or a conventional non-GSM cellular phone. In a network where you have one user-one number, this is desirable.
One concern of the users of such devices is that of privacy. Cordless phones now have simple forms of voice privacy which are proprietary to each manufacturer or specific model or phone. If cellular telephone is to become so pervasive as to begin to supplant normal wireline phones, using well defined, standard air interfaces, the privacy of these calls needs to be addressed.
There may arise many situations whereby there is only one communications device, but yet several people, each having their own number, wants that to be reached via that device. One example would be at home. One spouse may have a personal universal number, the other spouse yet another number, and perhaps another one for each teenage sons or daughters. In such a circumstance, it would be clearly undesirable for them each to have a unique phone that rings only their number when at home. In other situations such as, for example, a car pool situation, several people, each having their own SIM providing their own unique secure communications, may all wish to receive calls addressed to their individual SIM to be received on a single car phone.
It may be desirable for a person to have two universal numbers, one for personal communications, and one for work. It seems unlikely that it would be desirable to have a single number used for both work and a personal life, as these two different types of calls usually require different telephone mannerisms when first answering such calls. In such dual number cases, the personal number may be in force almost all the time, while the work number is used primarily at the office but occasionally at home or while in the car. In such case, it would be desirable for the user to be able to receive calls in secure communications mode for both numbers at once.
In another situation easiest understood by way of an example, a computer network person assigned to a help line may be on call for overnight or weekend emergency service. If the computer help line numbers is on a SIM, a computer network specialist could take that SIM home and place it in his home telephone coupled to the conventional wire line phone and receive help line calls there or in his car phone while driving around town, both using a secure mode of communications. However, at the same time he would like to be able to receive personal calls from his personal number.